This invention relates in general to valves for use in vehicle brake systems that utilize pressurized air, and in particular to a control valve for controlling the flow of pressurized air to the brakes of a vehicle.
Large commercial combination vehicles having a tractor portion and a trailer portion often include a vehicle braking system that utilizes compressed air. Air brake systems usually include a combination of three different braking systems: the service brakes, the parking brakes, and the emergency brakes. The service brake system applies and releases the brakes when the driver uses the brake pedal during normal driving situations. The parking brake system applies and releases the parking brakes when the parking brake control is engaged. The emergency brake system utilizes portions of the service brake and parking brake systems to stop the vehicle in the event of a brake system failure. Some air brake systems include a control brake valve that allows the operator to manually control the services brakes on the trailer portion of the vehicle independently of the tractor brakes. Such control valves are particularly useful in situations where a manually-controlled pressure graduation function is desired.
Control valves that are used for providing manually-controlled pressure gradation typically include a valve body that is attached to a handle which is used to operate or control the function of the valve. A spring or other biasing member may be incorporated into the valve to provide mechanical force for holding or retaining the valve handle in a first or closed position. Manually moving the handle from the first position to a second position typically causes the valve to change from a closed state to an open state. The valve will remain in the open state as long as the handle is held in the second position by the operator of the vehicle and will return to the closed state only when the handle is released. Continually holding the handle in the second or open position is often inconvenient and/or impractical for the operator; thus, there is a need for a locking mechanism that retains or holds the handle, and consequently the valve, in the second or open position and that does not involve continuous physical effort on the part of the vehicle's operator.